When dealing with wafers in the semi-conductor industry, it is important that the surfaces of the wafers be free from contamination. Wafer surfaces can be contaminated by various sources, including air-borne particulates, particles of semiconductor material removed during fabrication of the wafers or through the transportation or handling of the wafers. Such detritus may be found on either surface of the wafer. This detritus must be removed prior to using or further processing of the wafers to maintain the ultraclean conditions required for such uses.
U.S. Pat. No. 5,675,856 to Itzkowitz discloses a wafer scrubbing device which includes a pair of generally cylindrical brushes mounted on parallel shafts. In operation, each brush rotates around its own axis. The wafer is held between the brushes. A mechanism causes the brushes to extend back and forth radially across the surfaces of the wafer. At an extreme radial position, the cylindrical brushes engage only those portions of the wafer on one side of the center of the wafer. In this position, the rotating brushes apply a net torque around the center of the wafer, thereby imparting the wafer in rotation around its center. In another position, the brushes extend entirely across the wafer, so that the brushes apply no net torque on the wafer and the rotation of the wafer tends to stop. Thus, the radial movement of the brushes creates a speed differential between the constant rotational speed of the brushes and the variable rotational speed of the wafer.
However, such a mechanism is complex, costly and bulky. Thus, there is still a need for a wafer cleaning system which provides a simple and reliable means of subjecting all of the surfaces of the wafer to scrubbing.
The foregoing objects, features and various advantages of the present invention will be more readily apparent from the following detailed description of the preferred embodiments set forth below, taken in conjunction with the accompanying drawings.